1. Field of Invention
The present invention relates generally to methods and apparatus for stimulating hydrocarbon-bearing formations, i.e., to increase the production of hydrocarbon oil and/or gas from the formation, and more particularly to methods and apparatus for obtaining pressure below sealing elements in a wellbore completion.
2. Related Art
Hydrocarbons (oil, natural gas, etc.) are obtained from a subterranean geologic formation (i.e., a “reservoir”) by drilling a well that penetrates the hydrocarbon-bearing formation and thus causing a pressure gradient that forces the fluid to flow from the reservoir to the well. Often, well production is limited by poor permeability either due to naturally tight formations or due to formation damages typically arising from prior well treatment, such as drilling.
To increase the net permeability of a reservoir, it is common to perform a well stimulation treatment. A common stimulation technique consists of injecting an acid that reacts with and dissolves the formation damage or a portion of the formation thereby creating alternative flow paths for the hydrocarbons to migrate through the formation to the well. This technique known as acidizing (or more generally as matrix stimulation) may eventually be associated with fracturing if the injection rate and pressure is enough to induce the formation of a fracture in the reservoir.
In stimulation of oil and gas wells there is a need to acquire downhole information in real time to optimize the treatment of the well. This is especially true when compressible fluids, such as nitrogen or nitrified liquid, are pumped, since surface measurements may offer an inaccurate and delayed picture of what is happening downhole.
Current technologies enable acquisition of downhole measurements in real time during a job with a straddle packer. However, no tool on the market today provides measurements from below the bottom packer/element. A pressure measurement in this location, for instance, has the potential to add tremendous value to the operation, as it would indicate cross-flow between zones or leakage across the element.
Tubel Technologies, Inc., has a tool to take bottomhole pressure and temperature above the elements and transmit data acoustically. However, there is currently no known method and apparatus for taking measurements from below the bottom element, or for transmitting this pressure in real time to the surface.
Published Patent Applications US20050263281, WO2005116388, US20050236161 and WO2005103437 describe technology to communicate between downhole sensors and the surface to enable real time decision making based on accurate (0.01% accuracy) bottomhole pressure and temperature (1% accuracy) gauges, however, none of these references describe sensing pressure below a bottom sealing element of a packer and communicating this information to the surface, nor so they describe sensing pressure below a bottom sealing element of a packer during a well stimulation treatment and communicating this information to the surface, or using this information in real-time to make decisions during the stimulation, for example, to increase or decrease flow of a stimulation fluid.
From the above it is evident that there is a need in the art for new methods and new tools to measure pressure in real-time below a bottom packer element of a straddle packer, or below other flow sealing elements (such as chemical barriers) sealing the region being stimulated, and using this information in real-time or later.